1. Field of the Invention
This invention relates to an improvement of a spool type valve. More particularly, the invention relates to a spool type valve including a sleeve and a spool wherein the spool is received in the sleeve for slidable movement along the axis of the sleeve so as to open and close a port of the sleeve for the purpose of fluid control.
2. Prior Art
A spool type valve is conventionally known in the art which comprises a sleeve having a plurality of ports spaced apart along the axis thereof, and a spool having integral land portions for controllably opening and closing the ports of the sleeve. The spool is inserted into the sleeve for slidable movement along the axis thereof so as to define plural fluid passages in the sleeve. Such a spool type valve is used for the purpose of fluid control.
One prior art spool type valve employs an O-ring as a sealing member on the land. The O-ring is in slidable contact with the inner wall of the sleeve so as to seal the fluid passages.
It is noted, however, that the above spool type valve is designed so that the O-ring is slidably engaged directly with the inner wall of the sleeve. Accordingly, the O-ring tends to undesirably deform due to foreign material contained in oil or air, such as dust, powder caused from abrasion, for example, so that sealing ability is degraded during repetitive use of the spool type valve. It is also noted that immigration of foreign material into a space between the O-ring and the spool may cause undesirable lift-up of the O-ring.